Heretofore, the proportioning and dispensing of liquids has had to depend essentially upon batch mixtures of pre-measured ingredients, with their accompanying usual unused overage waste, if any degree of accuracy is required, or, upon aspirating hand sprayers where accuracy is immaterial. Moreover, aspiration and entrainment of a solute must be accomplished after discharge directly to the air to avoid backflow contamination condemned in most states.
The pressure upon the solute in conventional non-positive displacement type dispensers is vagrant. It can range rather widely down to a deep vacuum depending on the lift height from the solute supply or its controlled flow rate. Also, undesirable degradation of the ratio can occur in continuous flow mixes with any variation in the pressure of either the solvent or solute, or both, which sometimes occur with depletion. Although momentary or slight changes may not be serious because ratio accuracy can be objectionably degraded unless carefuly watched when using a municipal water supply system that might have a wide range of pressures and with different solute supplied stored in containers.
Rapid, accurate and reliable ratio and monitoring adjustments are desired but have not been available, particularly with the serious degradation of the ratio occurring with recurrent clogging of the solute supply or with proportioners of the aspirating type.
Moreover, when utilizing municipal water pressure, many continuous proportioning, instant mixing and dispensing devices can tolerate but very little pressure change without a correcting means because many municipal pressures are already quite low. Even a slight change can make a big difference in accuracy with wide variation in water pressure.
In correct those difficulties, the user must be able to monitor and control the ratio intermittently or continuously and accurately; the apparatus must be portable and readily viewed; should be easily readable and preferably utilize ambient light for illumination. Moreover, it should provide a continuously fresh sampling and quick read-out, if desired, to indicate any ratio degradations occurring and permit rapid null point traverse corrections.
Structurally and functionally, the instrument must be substantially attitude and altitude insensitive; capable of a self-purging of any foreign matter in all sections of its assembly, namely, the solvent and solute supply sections and the solution output sections; and, desirably, must be light, rugged, and easily handled.
Moreover, as disclosed in said Hechler applications, with the development of aspirating sprayers which are acceptable for utilizing various municipal water pressures because they do not create backflow contamination problems, a wide range of solutions at various ratios can now be applied, many of which due to potency or criticality require quite accurate ratio indication and control if control is possible.